Paper Explainer: Mapping Dark Matter Through the Dust of the Milky Way Part I

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Paper Explainer: Mapping Dark Matter Through the Dust of the Milky Way Part I

This is work that I did with my student, Eric Putney, then-Rutgers-postdoc Sung Hak Lim (now at the Institute for Basic Science in Daejeon), and my colleague David Shih. This is actually a continuation of work we’ve been doing for a while, starting with a paper that tested the idea on synthetic data, and then a later paper applying it to real data. I didn’t write blog posts on those because I fell behind on everything starting in 2020 and I’m only just now digging myself out. This new paper is one of a pair, Part II will be coming out in the new year.

So what’s the big idea, and what are we doing now?

In short, we have a new method that takes the motion of stars in the Milky Way and learns the gravitational potential of all the stars and gas and dark matter in the Galaxy. It does this even in the regions where we can’t see most of the stars, due to dust obscuring their light, which is the new development above and beyond the previous work. This paper is about the method, and the next paper will give the results for the gravitational potential and the dark matter density we can learn from it.

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Paper Explainer: Inferring the Morphology of the Galactic Center Excess with Gaussian Processes

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Paper Explainer: Inferring the Morphology of the Galactic Center Excess with Gaussian Processes

This is a paper I wrote with Tracy Slatyer at MIT, her student Yitian Sun (now a postdoc in McGill), Sidd Mishra-Sharma (previously a postdoc at IAIFI, newly hired as a professor at Boston University), and my student Ed Ramirez. I think it is fair to say Ed did the majority of the analysis and coding on this (quite extensive) project, and was instrumental to the project from beginning to end..

This paper is a contribution to a long-running debate within the fields of particle physics and astrophysics, so it is fairly technical in parts, but the debate itself is very interesting and — I think — very important for the field of dark matter.

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Paper Explainer: Force-feeding Supermassive Black Holes with Dissipative Dark Matter

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Paper Explainer: Force-feeding Supermassive Black Holes with Dissipative Dark Matter

There is a problem in the early Universe, one that demands an answer.

Or maybe there isn’t. But at least, there is something weird going on in the data, and as a theorist, that’s good enough for me.

JWST, our newest space telescope, is capable of peering back further into the history of the Universe than previously possible. Sensitive to the infrared (IR) wavelengths, it can see the earliest stars whose visible light has been redshifted into the IR by the expansion of the Universe. Among its many surprising discoveries, it has identified a population of “little red dots” — early galaxies with a perhaps surprising number of stars given how early they are forming and with evidence of supermassive black holes with high masses already formed in their galactic cores.

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Paper Explainer: Dark Radiation Isocurvature from Cosmological Phase Transitions

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Paper Explainer: Dark Radiation Isocurvature from Cosmological Phase Transitions

I want to tell you about my most recent paper “Dark Radiation Isocurvature from Cosmological Phase Transitions,” which I wrote with my coauthors Mitch Weikert, Peizhi Du, and Nicolas Fernandez. Peizhi and Nico are postdocs here at Rutgers, and Mitch is my grad student. All three are great and fun to work with, and you should hire them.

As the title of the paper suggests, this is a project with a bunch of moving parts, and it’s not easy (even by the standards of theoretical physics research) to explain to outsiders. Which is unfortunate, because it has to do with what we know about the very early Universe, and how we know it. It’s one of those things that is really beautiful and tremendously informative, but complicated enough that its hard to convey how and why we know the things we know.

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Paper Explainer: Via Machinae

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Paper Explainer: Via Machinae

This is an explainer for my most [recent paper][1], with my Rutgers colleague David Shih, Lina Necib at Caltech, and UCSC grad student (and a Rutgers undergrad alum) John Tamanas. It’s a project that we’ve been working on for a while (some of this being for obvious, 2020-related reasons), and I’m very happy to finally have it see the light of day, as it’s a really interesting convergence of a number of my interests in dark matter-motivated astrophysics, big data, and machine learning.

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Simulating a galaxy without a computer

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Simulating a galaxy without a computer

For particle physicists like myself, understanding how a galaxy works is critical for understanding how dark matter works at the particle level. All our evidence for the properties of dark matter, starting with its very existence and going from there, comes from its gravitational imprint on the visible matter. The physics of the very small influences the structure of some the largest objects in the Universe, and so by studying the latter, we learn about the former.

Which is why I’m going to share the story of an incredibly cool story of the earliest simulation of galaxies. Way back in 1941.

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Paper Explainer: Applying Liouville's Theorem to Gaia Data

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Paper Explainer: Applying Liouville's Theorem to Gaia Data

This is an explainer for my recent paper with David Hogg and Adrian Price-Whelan. This is a very different kind of paper for me, as evidenced by the fact that it is coming out on arXiv’s astro-ph (astrophysics) list and not even cross-listed to hep-ph (high energy phenomenology). In the end, the goal of the research that produced this paper is to learn about dark matter, but this paper by itself barely mentions the subject. There is a connection though.

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Paper Explainer: Direct Detection Anomalies in light of Gaia Data

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Paper Explainer: Direct Detection Anomalies in light of Gaia Data

This is an explainer for my recent paper with Gopolang (Gopi) Mohlabeng and Chris Murphy on the implications of recent surveys of dark matter velocity distributions from the Gaia mission on dark matter direct detection. There are a bunch of moving parts in this paper, as we’re trying to tie together some new directions from astrophysics with a long-standing problem in particle dark matter, so let me go through them.

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Paper Explainer: Asymmetry Observables and the Origin of RD^(∗) Anomalies

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Paper Explainer: Asymmetry Observables and the Origin of RD^(∗) Anomalies

This is an explainer of my recent paper, written with my colleague here at Rutgers David Shih, and David’s graduate student, Pouya Asadi. This is a follow-up in some sense to our previous collaboration, which for various reasons I wasn’t able to write up when it came out earlier this year.

This paper concerns itself with the RDRD and RD∗RD∗ anomalies, so I better start off explaining what those are. The Standard Model has three “generations” of matter particles which are identical except for their masses. The lightest quarks are the up and down, then the charm and strange, and finally the heaviest pair, the top and bottom. The electron has the muon and the tau as progressively heavier partners. The heavier particles can decay into a lighter version only through the interaction with a WW boson — these are the only “flavor changing” processes in the Standard Model.

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Paper Explainer: Gravitational probes of dark matter physics

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Paper Explainer: Gravitational probes of dark matter physics

The central thesis of the paper is that there is a huge potential to learn about the properties of dark matter: things like mass, interactions, production, etc using measurements from astronomy. This is not a completely novel idea: we know a great deal about dark matter from astronomy and cosmology (for example: dark matter is "cold" and not "hot"). However, there is an immense opportunity in the near future to do far more, thanks to improvements in simulation and some powerful new astronomical surveys which will be occurring. 

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Paper Explainer: An Update on the LHC Monojet Excess

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Paper Explainer: An Update on the LHC Monojet Excess

A few months ago, I wrote a paper with some other physicists at Rutgers: a graduate student Pouya Asadi, postdocs Anthony DiFranzo and Angelo Monteux (now a postdoc at UC Irvine), and my colleague David Shih. We had developed a new technique to sift through data from the two general purpose LHC experiments (ATLAS and CMS) to look for anomalies that could be the sign of new physics. While that paper was primarily about the technique, we had identified one possible excess, which we had dubbed the “mono-jet excess” since it was mainly found in LHC events with one jet of energy and significant amounts of missing momentum (characteristic of an energetic particle that doesn’t register in the LHC detectors). Here, we revisit that anomaly with more data and some ideas on how to determine if it is a real signal of new physics.

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Workshop talk: Mining LHC Data

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Workshop talk: Mining LHC Data

I'm at Fermilab for an LPC (LHC Physics Center) workshop on new ideas for LHC dark matter searches. I have been working with my fellow professor David Shih, postdocs Anthony DiFranzo and Angelo Monteux, and grad student Pouya Asadi at Rutgers on new ways to look for interesting anomalies in LHC data (see our paper and my blog post about it). Though not specifically about dark matter, it is a new idea, and so I have a talk about it. Here are the slides.

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TRISEP Summer School Lectures

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TRISEP Summer School Lectures

I'm up in Laurentian University in Sudbury, Ontario, giving three hours of lectures on "Beyond the Standard Model physics and the LHC" for the TRISEP Summer School.

TRISEP this year is mostly experimental grad students, and mostly experimental grad students working on experiments in the underground labs (such as SNOLAB in Sudbury). I'm the only lecturer who's talking about Beyond the Standard Model physics in general (though specific topics like dark matter and neutrino physics are being covered in more detail by other lecturers), and the only one talking about the LHC. Given that, and the audience, I ended up giving a broad overview: first on the sort of things we theorists have reason to think must exist beyond the Standard Model, then how the LHC works (always entertaining to have a theorist speak on how experiments work), and then lastly on how we look for new physics at the LHC. The slides are below.

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Paper Explainer: Digging Deeper for New Physics in the LHC Data

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Paper Explainer: Digging Deeper for New Physics in the LHC Data

Is there any new physics at the LHC?

The answer appears to be “no.” If there was obvious evidence of new physics at the LHC, trust me, you would have heard about it by now. 

But how do we know? The LHC produces a truly ridiculous amount of data. For each event (and the LHC writes to permanent record 400 events per second) the LHC records all information from all the detector elements. But nowhere in that information is a little flag that says “New Physics!” Indeed, most new physics we can imagine can be aped by physics of the Standard Model. We look for new physics via statistical evidence: we hope to see more events with a particular character than we would have expected. 

But we haven’t seen such an excess, correct?

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Paper Explainer: Collapsed Dark Matter Structures

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Paper Explainer: Collapsed Dark Matter Structures

This is a description of a paper I’ve written with my postdoc, Anthony DiFranzo. In our paper, we consider the possibility that dark matter could form gravitationally collapsed objects, evolving from an initial state of nearly uniform distribution across the Universe into one where it forms compact objects, analogous to have the regular matter that you and I are made of eventually formed stars and galaxies. Usually, we think this is not possible for dark matter, due to evidence that, on the largest scales, dark matter forms gravitationally bound structures that are much "fluffier" than the collapsed stars and galaxies. 

However, as we show in the paper, there is a way for dark matter to evolve into compact objects on small scales (say, a thousandth the size of the Milky Way), while still satisfying the constraints we've observed at larger scales. In demonstrating that it is possible for dark matter to do this, I think our paper makes an important point about some open questions in the field of dark matter research.

To explain why I started thinking about this particular project, I want to motivate it with a somewhat whimsical question.

Can there be planets and stars made of dark matter?

 

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Paper Explainer: Hiding Thermal Dark Matter with Leptons

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Paper Explainer: Hiding Thermal Dark Matter with Leptons

This is a description of my recent paper with my student David Feld. 

Dark matter is a problem. We know that there is a gravitational anomaly in galaxies: the stuff we can see is moving far too fast to be held together by its own gravity. Add to this the precision measurements of the echoes of the Big Bang (the Cosmic Microwave Background), which tells us that the way the Universe was expanding and matter was clumping cannot be explained without some new stuff that didn’t interact with light, and you have very solid evidence for the existence of dark matter. Then of course, there is the Bullet Cluster, where we can see the gravitational imprint of dark matter directly.

So we know it exists. We just don’t know what it is.

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